This invention relates to organic polymers, particularly organic polymers containing dispersed reinforcing agents.
It is well known to reinforce organic polymers with macroscopic fillers such as glass, polyamide, polyester, graphite or similar fibers; particulate fillers such as calcium carbonate, barium sulfate and the like, and other fillers such as sand, and milled or flaked glass. Although these fillers are known to improve the properties of the polymer, they have several drawbacks. One is the amount of such fillers which are needed to obtain good reinforcement.
Typically, up to about 60 percent or more of the filled polymer comprises the filler material. It would be highly desirable to obtain good reinforcement at lower levels of filler. Another problem is that many of these filler materials do not strongly adhere to the polymer matrix. Accordingly, the reinforcement is not as great as would be expected. Another problem is that although certain properties such as modulus and tensile strength are improved by the use of these fillers, these improvements are usually accompanied by a substantial decrease in other properties, notably impact strength, fatigue and elongation.
It is known to reinforce certain types of polymers, notably polyurethanes, with colloidally dispersed polymer particles. These systems are exemplified by the so-called "polymer polyols" used in polyurethane production, which generally contain as the dispersed polymer a styrene/acrylonitrile copolymer, a polyurea polymer or a polyurethane-urea polymer. The dispersed polymers are usually prepared in situ by polymerizing the appropriate monomers within the polyol. The reinforced polyurethane is prepared by reacting the dispersion with a polyisocyanate. The use of polymer polyols has not been found to significantly increase properties such as tensile strength or flexural modulus. The major use for these products has been in flexible polyurethane foams, where the dispersed particles increase the load bearing properties of the foam, and perform a cell opening function.
It is also known to improve the impact properties of thermoplastics such as styrene by dispersing therein minute particles of rubbery substances such as polybutadiene or acrylonitrile/butadiene copolymers. These particles are often grafted to the continuous phase in order to further improve physical properties.
It would be desirable to provide a reinforced polymer in which good reinforcement is obtained even at relatively low filler levels and in which desirable improvements in physical properties are achieved without major losses in other properties.